Really need your help ladies I’m so worried, basically yesterday morning I woke up in a lot of pain…

Really need your help ladies I’m so worried, basically yesterday morning I woke up in a lot of pain in my left boob it was on one side of my boob it feels like a really big lump. As the day progressed the pain got worse and worse and I started to feel really ill, I felt drowsy, my whole body started to ache and I felt so cold even though my partner said I was on fire. I felt I was going to be sick and had the worse headache that lasted the whole day, I couldn’t eat anything apart from a bite of toast and even that made me feel really sick. I’ve woken up today still in pain and now my back and neck are hurting / aching too. I’m going to try and get a doctors appointment today but would love to know if anyone has experienced anything like this as I have never felt like this before. I am currently breastfeeding but only with one boob ( long story ) but I haven’t used my left one for at least a month and half so I don’t think it’s milk blocked up as when I did use it barely anything came out maybe a few drops?? But I spoke to health visitor and she said it’s perfectly fine just to use the one, thanks ladies xxx